KVM: x86: Rename "SF" macro to "SCATTERED_F"

Now that each feature flag is on its own line, i.e. brevity isn't a major
concern, drop the "SF" acronym and use the (almost) full name, SCATTERED_F.

No functional change intended.

Link: https://lore.kernel.org/r/20241128013424.4096668-55-seanjc@google.com


Signed-off-by: Sean Christopherson <seanjc@google.com>